1. Field of the Invention
The present invention relates to an optimal-writing method, medium and apparatus and more particularly, for maintaining an optimal writing power for various recording modes during data recording onto a recording medium.
2. Description of the Background Art
A disk device being capable of recording data onto a disk recording medium always conducts an OPC (Optimal Power Calibration) at a PCA (Power Calibration Area) to determine an optimal writing power before writing input data onto a disk recording medium. The determined optimal writing power is used to write user data inputted from an external source onto a disk recording medium.
During data recording, a recording position advances outward. However, the characteristics of a recording layer changes from inner radius to outer radius. Therefore, although data is recorded with the obtained optimal writing power, the quality of a reproduced signal may not be preserved at the outer radius.
Due to the centrifugal force in the spin coating process, the thickness of the created recording layer tends to increase from the inner radius to outer radius.
Unless the thickness of the recording layer is uniform over the disk, the response of the recording layer to an applied writing laser beam differs according to the thickness. As the thickness of the recording layer increases, the extent to which the recording layer is burnt by the writing beam decreases and thus the reflection ratio of burnt marks increases. As a result, characteristic of reproduced signals deteriorate as the position moves outward.
To overcome such a problem, a disk device detects a reflected level (called ‘B-level’) as a reference when a writing pulse has been stabilized after a medium change, and controls the writing power adaptively to make the B-level detected during data recording equal to the previously-detected reference (See FIG. 1). This operation is called ROPC (Running Optimal Power Control).
A disk device may data on a disk recording medium at low enough a speed such that a medium characteristic is fully changed by a writing pulse. The recording mode so used is called ‘CLV’ (Constant Linear Velocity) shown in FIG. 2a. The recording speed is same at all positions on a recording medium in CLV mode.
However, technology development has introduced a P-CAV (Partial Constant Angular Velocity) recording mode in which recording speed increases gradually up to a maximum recording speed as a recording position moves outward and a recording mode is changed to CLV the moment recording speed reaches the maximum, as shown in FIG. 2b. Due to the P-CAV mode, the overall recording speed is increased.
Recording technology has made higher recording speeds possible by full CAV in which recording is conducted under constant rotational speed on an entire recording area as shown in FIG. 2c. If a user requests the fastest recording speed, user data are recorded in full CAV.
However, if a recording speed changes (during data recording), from the speed at which B-level reference was detected, the ROPC can not ensure an optimal writing power. Therefore, it is necessary for a disk recording device to adapt ROPC to various recording modes and to improve ROPC to cope with changes in recording speed.